Ice Cream in a Bag

Deanna Cullen | Mon, 04/28/2014 - 13:10

A quick google search will allow you to find many laboratory activities for making ice cream in chemistry class. Some of the links provide questions to incorporate into the activity. I have used several over the years and will share my modified version here.

If cost is an issue, you can ask students to bring in items. I add 3 tablespoons of vanilla directly to a gallon of whole milk before the lab so that students don't have to add it individually. We share the ice/salt bags between two students. I enjoy having fun with my students while working through this activity, but the discussion we have before and after making the ice cream is important to make sure the students understand WHY we are making ice cream. I hesitate to have my students eat in the laboratory setting. I suggest that teachers find an alternative room. My laboratory is a separate room, so I can have students complete the activity in my classroom or sign up for our school's all-purpose room which is equipped with kitchen appliances.

This is also a great outreach activity for ChemClub, scouts or other venues.

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Concepts:

colligative properties

Time required:

45 minutes

Materials:

per class of 30

One gallon whole milk

3-4 Tbsp vanilla

Two cups sugar

One 4-lb box of ice cream salt (if sharing ice/salt bag in pairs)

30 pint size freezer bags

15 quart size freezer bags (if sharing in pairs)

30 spoons

10 pounds of ice

Background:

Many energy transfers take place when making ice cream in baggies. One is between the ice and salt. Another is between the ice/salt mixture and the ice cream. Your hands will get cold during the mixing, so don't forget that transfer.

Procedure:

1.

Pint freezer bag: (You may each make one of these and put both into the ice/salt mixture…to share the effort of shaking the bags.) Add the following ingredients and zip (try not to leave any air space). Make sure you have a tight seal. (If salt gets into the ice cream…it will taste bad!)

½ cup whole milk, 1 Tbsp Sugar, ¼ tsp. vanilla

2.

Fill a quart size freezer bag ½ full of ice. Record the temperature of the ice. Also record the room temperature.

3.

Add ½ cup of ice cream salt to the ice. Place the pint size freezer bag into the quart size freezer bag and seal the bag carefully (remove as much air as you can).

4.

After 10 minutes, remove the smaller freezer bag and wipe the salty water from it. Record the temperature of the ice/salt.

5.

Open the ice cream bag and taste if you would like.

6.

Dispose of ice mixture in the sink. Throw everything else in the trash.

Questions:

Post-Lab Questions:

1.

Is freezing an exothermic or endothermic process?

2.

Why did the outside of the bag get wet? (assume that your bag did not leak)

3.

Describe the transfers of energy that occurred in this lab.

a.

Between air and bag.

b.

Between ice/salt bag and ice cream.

c.

Any others?

4.

What happened shortly after you added the salt to the ice cubes? Was the temperature above or below the freezing point temperature for water?

5.

What does this tell you about the freezing point temperature of salt water compared to fresh water?

6.

Ice cream doesn’t freeze solid at 0°C. Why not?

7.

In the radiator of your car you put a combination of antifreeze and water to keep your car engine cool in the summer and prevent the radiator from freezing in the winter. Explain how you think this works in terms of what you saw in the experiment you just did.

Preparation:

Add 3 Tbsp of vanilla to a gallon of whole milk

Obtain materials, including ice

Attribution:

You can find many ice cream labs on line. I originally used a lab that I picked up during professional development (with no author name) and I have modified to my own version over time.